Happiness Is Contagious

New research from Harvard Medical School and the University of California, San Diego suggests that happiness is influenced not only by the people you know, but by the people they know.

The study showed that happiness spreads through social networks, sort of like a virus, meaning that your happiness could influence the happiness of someone you've never even met.

Sadness spreads too, but much less efficiently, says study co-author James H. Fowler, PhD, of the University of California-San Diego.

"We have known for a long time that there is a direct relationship between one person's happiness and another's," Fowler tells WebMD.

"But this study shows that indirect relationships also affect happiness. We found a statistical relationship not just between your happiness and your friends' happiness, but between your happiness and your friends' friends' friends' happiness."

Three Degrees of Separation

Fowler and Harvard social scientist Nicholas Christakis, MD, PhD, have been studying social networks for several years, using data from the ongoing Framingham Heart Study.

Last year the pair made headlines when they reported that obesity seems to spread through social groups, so that your chances of becoming overweight are greater when your friends and their friends gain weight.

A related study, published earlier this year, found that smokers were more likely to give up cigarettes when their family, friends, and other social contacts stopped smoking.

Their latest research, published today online in the journal BMJ, was designed to determine whether happiness spreads through social networks in a similar way.

The researchers were able to recreate the social networks of 4,739 Framingham participants whose happiness was measured from 1983 to 2003. A standard test for assessing happiness was used, which included questions like "I felt hopeful about the future," and "I was happy."

Important family changes for each participant -- such as a birth, death, marriage, or divorce -- were also recorded. The participants were also asked to name family members, close friends, co-workers, and neighbors.

Because many of these contacts were also study participants, the researchers were able to identify more than 50,000 social and family ties and analyze the spread of happiness through the group.